CN111561694B - Method and system for improving low-load SCR inlet smoke temperature of coal-fired boiler - Google Patents

Method and system for improving low-load SCR inlet smoke temperature of coal-fired boiler Download PDF

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CN111561694B
CN111561694B CN202010496436.XA CN202010496436A CN111561694B CN 111561694 B CN111561694 B CN 111561694B CN 202010496436 A CN202010496436 A CN 202010496436A CN 111561694 B CN111561694 B CN 111561694B
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coal
burner
layer
secondary air
target
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CN111561694A (en
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童家麟
齐晓娟
王文欣
孙五一
吕洪坤
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Electric Power Research Institute of State Grid Zhejiang Electric Power Co Ltd
Zhejiang Energy Group Research Institute Co Ltd
Hangzhou E Energy Electric Power Technology Co Ltd
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Electric Power Research Institute of State Grid Zhejiang Electric Power Co Ltd
Zhejiang Energy Group Research Institute Co Ltd
Hangzhou E Energy Electric Power Technology Co Ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C5/00—Disposition of burners with respect to the combustion chamber or to one another; Mounting of burners in combustion apparatus
    • F23C5/08—Disposition of burners
    • F23C5/10—Disposition of burners to obtain a flame ring
    • F23C5/12—Disposition of burners to obtain a flame ring for pulverulent fuel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C5/00—Disposition of burners with respect to the combustion chamber or to one another; Mounting of burners in combustion apparatus
    • F23C5/08—Disposition of burners
    • F23C5/24—Disposition of burners to obtain a loop flame
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C5/00—Disposition of burners with respect to the combustion chamber or to one another; Mounting of burners in combustion apparatus
    • F23C5/08—Disposition of burners
    • F23C5/28—Disposition of burners to obtain flames in opposing directions, e.g. impacting flames
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C7/00—Combustion apparatus characterised by arrangements for air supply
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C7/00—Combustion apparatus characterised by arrangements for air supply
    • F23C7/008—Flow control devices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N1/00—Regulating fuel supply
    • F23N1/02—Regulating fuel supply conjointly with air supply
    • F23N1/022—Regulating fuel supply conjointly with air supply using electronic means

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  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Regulation And Control Of Combustion (AREA)

Abstract

The invention discloses a method and a system for improving the smoke temperature at the low-load SCR inlet of a coal-fired boiler. The method adopted by the invention comprises the following steps: spraying the fire coal of the tangential firing or opposed firing boiler into a hearth for combustion by taking a layer as a unit; the coal quantity of each burner layer is gradually increased from low to high along the height direction of the hearth to form positive V-shaped distribution; the secondary air volume of each burner layer is gradually reduced from low to high along the height direction of the hearth to form inverted V-shaped distribution; and meanwhile, the adjustable shrinkage hole opening of the pulverized coal pipe and the opening of the secondary air door of each combustor or the angle of a secondary air blade are controlled, so that the coal quantity and the secondary air quantity of each combustor of the operating combustor layer reach the target coal quantity and the target secondary air quantity. The invention can reduce NO to the outlet of the hearth as much as possible by adjusting the coal amount and the secondary air distribution of each burner of the operating burner layerXOn the premise of influence of the content and the pulverized coal burnout rate, the low-load SCR inlet flue gas temperature is effectively increased.

Description

Method and system for improving low-load SCR inlet smoke temperature of coal-fired boiler
Technical Field
The invention belongs to the technical field of utility boilers, and particularly relates to a method and a system for improving the low-load SCR inlet smoke temperature of a coal-fired boiler.
Background
With the increase of the energy structure adjustment speed in China, clean energy enters a new stage of large-scale development, renewable energy sources such as hydropower, wind power and photovoltaic are used for large-scale grid connection, the peak-valley difference of a power grid system is increased, and under the condition that the existing peak regulation resources are relatively insufficient, a coal-fired thermal power generating unit carries out deep low-load peak regulation operation and has the load regulation performance as fast as possible.
The deep peak regulation low-load operation capability of the coal-fired thermal power unit is limited in many aspects, the stable operation capability of a Selective Catalytic Reduction (SCR) system is one important index for considering whether the unit has the deep peak regulation capability or not, in the prior art, combustion modes of equal coal distribution and equal air distribution are often adopted for each operating combustor layer when the coal-fired thermal power unit operates at low load, the problem of uneven air distribution of each combustor of the operating combustor layer exists due to a secondary air box structure of an opposed firing boiler, the stable operation of the SCR system is influenced due to the fact that the smoke temperature at the inlet of the SCR is low and the smoke temperature deviation is large during low load, and the deep peak regulation low-load operation capability of the coal-fired thermal power unit is limited undoubtedly.
Disclosure of Invention
In view of the above, the invention provides a method and a system for improving the low-load SCR inlet smoke temperature of a coal-fired boiler, which take a domestic common tangential firing or opposed firing boiler as a research object and can reduce NO at the outlet of a hearth as much as possibleXOn the premise of influence of the content and the pulverized coal burnout rate, the low-load SCR inlet flue gas temperature is effectively increased.
In order to achieve the purpose, the invention provides the following technical scheme: a method of increasing low load SCR inlet flue gas temperature of a coal fired boiler, comprising:
spraying the fire coal of the tangential firing or opposed firing boiler into a hearth for combustion by taking a layer as a unit;
calculating the coal quantity of each delivery burner layer according to a target coal quantity calculation formula of each delivery burner layer;
adjusting the coal quantity of each operating burner layer to ensure that the coal quantity of each burner layer is gradually increased from low to high along the height direction of the hearth to form positive V-shaped distribution;
calculating the secondary air volume of each operating burner layer according to a target secondary air volume calculation formula of each operating burner layer;
adjusting the secondary air volume of each operating burner layer to ensure that the secondary air volume of each burner layer is gradually reduced from low to high along the height direction of the hearth to form inverted V-shaped distribution;
calculating the coal amount of each burner according to a target coal amount calculation formula of each burner of the commissioning burner layer;
additionally arranging an electric valve on an adjustable shrinkage hole on each pulverized coal pipe of the commissioning combustor layer, and controlling the opening of the adjustable shrinkage hole to enable the coal amount of each combustor of the commissioning combustor layer to reach the target coal amount;
calculating the secondary air quantity of each burner according to a target secondary air quantity calculation formula of each burner of the commissioning burner layer;
and controlling the opening degree of each burner secondary air door or the angle of a secondary air blade of each burner of the commissioning burner layer to enable the secondary air quantity of each burner of the commissioning burner layer to reach the target secondary air quantity.
Further, the calculation formula of the target coal amount of the nth burner layer is as follows: cn＝C1αn，
Figure BDA0002523043970000021
n∈[1,4]Wherein, C1Indicates the target amount of coal, C, in the layer 1 combustor layernIndicates the target coal amount, alpha, of the burner floor of the nth floornA coefficient of deviation, C, of the target coal amount of the burner floor of the n-th floor from the target coal amount of the burner floor of the 1 st floorzRepresenting the total coal required by the boiler and n representing the number of layers of the operating burners.
Further, the calculation formula of the target coal amount of each burner of the nth burner layer is as follows: c. Cm＝Cn/m，m∈[1,4](ii) a Wherein m is the number of burners of the nth burner.
Further, the calculation formula of the target secondary air volume of the nth burner layer is as follows: fn＝(Cnβn-Cnγn)τn，n∈[1,4](ii) a Wherein, FnRepresents the target secondary air quantity, beta, of the nth burner layernRepresents the theoretical air quantity, gamma, of the burner layer of the n-th layernDenotes the air/coal ratio, tau, in the primary air-powder mixture of the n-th burner layernThe excess air factor of the nth burner layer is shown.
Furthermore, the calculation formula of the target secondary air volume of each burner of the nth burner layer is as follows: f. ofm＝Fn/m，m∈[1,4](ii) a Wherein m is the number of burners of the nth burner.
Further, the calculation formula of the total air volume of the boiler is as follows: fz＝CzβzτzWherein F iszRepresents the total air quantity of the boiler, betazIndicating theoretical amount of air, τ, of the boilerzRepresenting the boiler excess air factor.
Further, the calculation formula of the burn-out air volume is as follows:
Figure BDA0002523043970000031
wherein, FrThe burn-out air volume is indicated.
The invention takes a relatively common tangential firing or opposed firing boiler at home as a research object, and can reduce NO to the hearth outlet as much as possibleXOn the premise of influence of the content and the coal powder burnout rate, the flue gas temperature at the inlet of the low-load SCR is effectively improved by adjusting the coal quantity and the secondary air quantity distribution of each combustor of the operating combustor layer.
The invention also provides another technical scheme: a system for improving the smoke temperature at the low-load SCR inlet of a coal-fired boiler comprises a layering unit, a coal quantity control unit, a coal quantity metering unit, a secondary air quantity control unit and a secondary air quantity metering unit;
the layering unit sprays the fire coal of the tangential firing or opposed firing boiler into the hearth for combustion by taking the layer as a unit;
the coal quantity control unit controls the output of each coal feeder and further controls the coal quantity of the operating burner layer, so that the coal quantity of each burner layer is gradually increased from low to high along the height direction of the hearth to form positive V-shaped distribution;
the secondary air quantity control unit controls the total secondary air door of each commissioning combustor layer so as to control the secondary air quantity of each commissioning combustor layer, so that the secondary air quantity of each combustor layer is gradually reduced from low to high along the height direction of the hearth, and inverted V-shaped distribution is formed;
the coal quantity metering unit controls the opening of the adjustable shrinkage cavity, so that the coal quantity of each burner of the commissioning burner layer reaches the target coal quantity;
and the secondary air quantity metering unit controls the opening degree of a secondary air door or the angle of a secondary air blade of each burner of the delivery burner layer, so that the secondary air quantity of each burner of the delivery burner layer reaches the target secondary air quantity.
Further, the coal amount metering unit comprises a coal amount calculating unit, a coal amount measuring unit and a coal amount adjusting unit;
the coal amount calculating unit is used for calculating the coal amount of each pulverized coal pipe through a target coal amount calculating formula of a commissioning combustor layer and a target coal amount calculating formula of each combustor of the commissioning combustor layer;
the coal quantity measuring unit is additionally provided with a coal quantity measuring device on each pulverized coal pipe to measure the coal quantity of each pulverized coal pipe in real time;
the coal quantity adjusting unit adjusts the coal quantity of each pulverized coal pipe in real time by adjusting the opening of the electric valve on the adjustable shrinkage cavity of each pulverized coal pipe.
Further, the secondary air quantity metering unit comprises a secondary air quantity calculating unit, a secondary air quantity measuring unit and a secondary air quantity adjusting unit;
the secondary air quantity of each burner is calculated by the secondary air quantity calculating unit through a target secondary calculating formula of the operating burner layer and a target secondary air quantity calculating formula of each burner of the operating burner layer;
the secondary air quantity measuring unit is additionally provided with a secondary air quantity measuring device at a secondary air nozzle of each burner, and the secondary air quantity of each burner is measured in real time;
and the secondary air quantity adjusting unit adjusts the secondary air quantity of each combustor in real time by adjusting the opening degree of a secondary air door or the angle of a secondary air blade of each combustor.
According to the invention, the coal quantity of each operating burner layer is adjusted, so that the coal quantity of each burner layer is gradually increased from low to high along the height direction of the hearth to form positive V-shaped distribution; and adjusting the secondary air volume of each operating burner layer to ensure that the secondary air volume of each burner layer is gradually reduced from low to high along the height direction of the hearth to form inverted V-shaped distribution, namely a V-shaped combustion mode.
Compared with the prior art, the system can reduce NO to the outlet of the hearth as much as possible by adjusting the coal quantity and the secondary air quantity distribution of each burner of the put-in-service burnerXOn the premise of influence of the content and the pulverized coal burnout rate, the low-load SCR inlet flue gas temperature is effectively increased.
Drawings
FIG. 1 is a schematic diagram showing the distribution of coal amount and secondary air volume in each operating burner layer, for example, a boiler with 4X 6 layers of burners at 40% rated load in the prior art (FIG. 1a is a coal supply amount diagram, and FIG. 1b is a secondary air amount diagram);
FIG. 2 is a flow chart of a method of increasing the inlet flue gas temperature of a low load SCR of a coal fired boiler in accordance with an embodiment of the present invention;
FIG. 3 is a schematic diagram showing the coal quantity and the secondary air quantity distribution of each operating burner layer under the condition of the method of the present invention by taking a boiler of a 4X 6 layer burner as an example at 40% rated load according to the embodiment of the present invention (FIG. 3a is a coal feeding quantity diagram, and FIG. 3b is a secondary air quantity diagram);
FIG. 4 is a schematic diagram showing the distribution of the coal amount and the secondary air volume of each operating burner of the 1 st burner layer at 40% rated load according to the embodiment of the present invention (FIG. 4a is a coal supply amount diagram, and FIG. 4b is a secondary air volume diagram);
FIG. 5 is a schematic structural diagram of a system for increasing the inlet flue gas temperature of a low-load SCR of a coal-fired boiler according to an embodiment of the present invention.
Detailed Description
The following detailed description of the embodiments of the present invention is provided in connection with the accompanying drawings for the purpose of facilitating understanding and understanding of the technical solutions of the present invention. It is to be understood that the specific embodiments described herein are merely illustrative of some, but not all, embodiments of the invention and that other embodiments may be devised by those skilled in the art without the use of the inventive faculty and the scope of the invention is to be protected.
Example 1
The embodiment provides a method for improving the low-load SCR inlet smoke temperature of a coal-fired boiler, which takes a relatively common tangential firing or opposed firing boiler in China as a research object and can reduce NO to the hearth outlet as much as possibleXOn the premise of influence of the content and the pulverized coal burnout rate, the flue gas temperature at the inlet of the low-load SCR is effectively improved by adjusting the coal quantity and the secondary air quantity distribution of each burner of the operating burner layer; after the adjustment according to the invention, the coal quantity of each layer of the combustor is gradually increased from low to high along the height direction of the hearth to form positive V-shaped distribution; meanwhile, the secondary air volume of each burner layer is gradually reduced from low to high along the height direction of the hearth to form inverted V-shaped distribution; this is called "V-shaped combustion system".
Fig. 2 is a flow chart of a method for increasing the flue gas temperature at the inlet of the low-load SCR of the coal-fired boiler according to the embodiment of the present invention. The invention discloses a method for improving the low-load SCR inlet smoke temperature of a coal-fired boiler, which mainly takes a relatively common tangential firing or opposed firing boiler at home as a research object, adjusts the coal quantity and the secondary air quantity distribution of each burner of a commissioning burner layer in a novel mode, and mainly aims to improve the low-load SCR inlet smoke temperature of the coal-fired boiler and simultaneously reduce NO to the outlet of a hearth to the greatest extentXThe method comprises the following specific steps:
step 1: spraying the fire coal of the tangential firing or opposed firing boiler into a hearth for combustion by taking a layer as a unit;
step 2: calculating the coal quantity of each delivery burner layer according to a target coal quantity calculation formula of each delivery burner layer;
and step 3: adjusting the coal quantity of each operating burner layer to ensure that the coal quantity of each burner layer is gradually increased from low to high along the height direction of the hearth to form positive V-shaped distribution;
and 4, step 4: calculating the secondary air volume of each operating burner layer according to a target secondary air volume calculation formula of each operating burner layer;
and 5: adjusting the excess control coefficient of each operating burner layer to ensure that the excess control coefficient of each layer of burners is gradually reduced from low to high along the height direction of the hearth to form inverted V-shaped distribution;
step 6: calculating the coal amount of each burner according to a target coal amount calculation formula of each burner of the commissioning burner layer;
and 7: additionally arranging an electric valve on an adjustable shrinkage hole on each pulverized coal pipe of the commissioning combustor layer, and controlling the opening of the adjustable shrinkage hole to enable the coal amount of each combustor of the commissioning combustor layer to reach the target coal amount;
and 8: calculating the secondary air quantity of each burner according to a target secondary air quantity calculation formula of each burner of the commissioning burner layer;
and step 9: and controlling the opening degree of each burner secondary air door or the angle of a secondary air blade of each burner of the commissioning burner layer to enable the secondary air quantity of each burner of the commissioning burner layer to reach the target secondary air quantity.
After the above steps, if the furnace outlet NO isXIf the content is increased, adjusting the NO at the outlet of the hearth by means of adjusting the air distribution of the over-fire air burner and the likeXAnd (4) content.
If the burnout rate of the pulverized coal is reduced to some extent, the fineness of the pulverized coal at the outlet of the coal mill is adjusted by optimizing the opening of a folding baffle at the outlet of the coal mill, the rotating speed of a rotary separator, the loading force of a grinding roller and the like.
In order to realize the purpose of the invention, the coal quantity and the secondary air quantity of each pulverized coal pipe need to be measured, the coal quantity can be additionally arranged on each pulverized coal pipe by adopting proper measures, the secondary air quantity measuring device is additionally arranged at the secondary air injection port of each burner for real-time measurement, the adjustable shrinkage hole of each pulverized coal pipe is additionally provided with an electric valve, and the secondary air door or the secondary fan blade of each burner is additionally provided with an electric valve for real-time adjustment.
The invention is operated as an example with a subcritical 600MW four-corner tangential firing boiler of 40% rated load, and the boiler is a 4 x 6 layer burner. In general, this boiler is operated with 4-tier burners, i.e., 4 × 4-tier burners, at 40% rated load, the operation burners are of a uniform coal distribution and uniform air distribution combustion system, and the distribution of the coal quantity and the secondary air flow in the operation burners is roughly as shown in fig. 1. The approximate conditions of the coal quantity and the secondary air quantity distribution of the burner layer in operation by the method for improving the smoke temperature of the low-load SCR inlet of the coal-fired boiler are shown in figure 3.
In FIG. 1 and FIG. 3, the amounts of coal in 1 to 4 layers of burners are represented by C1、C2、C3、C4Expressed in units of t/h.
In FIGS. 1 and 3, the deviation coefficients of the coal amounts of the burner layers of 2, 3 and 4 and the burner layer of 1 st in terms of α2、α3、α4Denotes, in general, α in FIG. 12＝α3＝α4The value of fig. 3 varies according to the study subject, about 1.1-1.3, and the NO at the exit of the furnace should be considered comprehensivelyXThe content, the coal powder burnout rate and other factors are determined, and for the method for improving the low-load SCR inlet smoke temperature of the coal-fired boiler, the alpha value is2<α3<α4。
In FIG. 1 and FIG. 3, the theoretical air amount of 1 to 4 burner layers is represented by β1、β2、β3、β4Expressed in units of t/h dry air/t/h coal.
In FIG. 1 and FIG. 3, the air/coal ratio of the primary air-powder mixture in 1-4 burner layers is gamma1、γ2、γ3、γ4Expressed in units of t/h dry air/t/h coal.
In FIGS. 1 and 3, the excess of 1 to 4 burner layersAir coefficient in τ1、τ2、τ3、τ4The values of the expression are different according to different research objects, and the NO of the furnace outlet is consideredXAfter the content is determined, the value is between 0.6 and 1.4, and tau is determined for the method for improving the low-load SCR inlet smoke temperature of the coal-fired boiler1>τ2>τ3>τ4。
For the boiler, the invention provides a calculation formula of target coal quantity and target secondary air quantity of each burner of a running burner layer:
Cn＝C1αn，n∈[1,4]
Figure BDA0002523043970000081
cm＝Cn/m，n∈[1,4]，m∈[1,4]，
Fn＝(Cnβn-Cnγn)τn，n∈[1,4]，
fm＝Fn/m，n∈[1,4]，m∈[1,4]
and according to the formula and the values of the coal quantity deviation coefficient and the excess air coefficient of different research objects, the target coal quantity of each pulverized coal pipe can be calculated under the condition of determining the total secondary air quantity of the operating combustor layer.
For the boiler, the invention also provides a calculation formula of the target total air volume and the target burn-out air volume:
Fz＝Czβzτz，
Figure BDA0002523043970000082
wherein, betazIs the theoretical amount of air, τ, in the boilerzIs the boiler excess air factor. For deep peak-shaving low-load operation of coal-fired boilerzThe value is between 1.2 and 1.3.
For this type of boiler, when operating at 40% of rated load, the typical coal distribution for each pulverized coal pipe of the operating burner floor is shown in the upper half of fig. 1, and the typical secondary air distribution is shown in the lower half of fig. 1.
For this type of boiler, when it is operated at 40% of rated load, the improved combustion concept according to the present invention is shown in fig. 3, the coal quantity of each layer of burners is gradually increased from low to high along the height direction of the furnace, forming a "positive V" shaped coal quantity distribution; the secondary air volume of each burner layer is gradually reduced from low to high along the height direction of the hearth to form inverted V-shaped secondary air volume distribution, and the inverted V-shaped secondary air volume distribution are used for practice at the same time to form a V-shaped combustion mode.
Comparing the combustion concepts of fig. 1 and fig. 3, it can be known that the "V-shaped combustion mode" is more concentrated in the coal amount to be fed into the upper burner than the conventional combustion mode, and the secondary air volume in the area is reduced, and the pulverized coal combustion in the area is delayed, so that the flame center in the boiler furnace chamber adopting the "V-shaped combustion mode" is obviously improved, which is beneficial to improving the flue gas temperature at the SCR inlet.
The coal quantity of the upper burner layer of the hearth of the V-shaped combustion mode is increased compared with that of the conventional combustion mode, and the secondary air quantity is reduced, so that the staged combustion effect of the boiler is weakened, and the possibility of causing NO at the outlet of the hearthXThe content is increased.
In addition, the coal quantity of the burner layer on the upper part of the hearth of the V-shaped combustion mode is increased compared with the conventional combustion mode, and the secondary air quantity is reduced, so that the combustion of the pulverized coal is delayed, the retention time in the hearth is reduced, and the burnout rate of the pulverized coal is possibly adversely affected.
To control the "V-shaped combustion mode" may cause the furnace outlet NOXThe invention can optimize the air distribution of each burner of the over-fire air according to the actual condition.
In order to control the problem of coal powder burnout rate reduction possibly caused by the implementation of a V-shaped combustion mode, the invention can optimize the opening of the folding baffle plate at the outlet of the coal mill, the rotating speed of the rotary separator and the loading force of the grinding roller according to the actual condition.
Taking a No. 1 boiler of a certain power plant as an example, the boiler is a subcritical, single reheating, forced circulation, balanced ventilation, single steam drum and semi-open 2008t/h four-corner tangential firing pulverized coal fired boiler, and is configured with 24 layers of 6 low NO boilersXBurners for further reduction of NOXAnd exhausting, wherein the boiler is also provided with an over-fire air nozzle at the upper part of the main burner. The design coal type of the boiler is shown in table 1.
If the coal type is designed, the coal amount of the boiler is about 112t/h when the boiler operates at 40% rated load. Under the conventional combustion mode, the distribution of the coal quantity and the secondary air quantity of the operating combustor is shown in the upper half part and the lower half part of the graph 1.
TABLE 1 boiler design coal type coal quality analysis
Figure BDA0002523043970000091
Figure BDA0002523043970000101
Under the design of coal types, when the boiler operates at 40% rated load, the distribution of the coal quantity and the secondary air quantity of the operating burner layer in a V-shaped combustion mode is shown in the upper half part and the lower half part of a graph 3, and the distribution of the coal quantity and the secondary air quantity of each burner of the operating burner layer is shown in the upper half part and the lower half part of a graph 4.
For this boiler, with the combustion method of the present invention, the coal amount deviation coefficient: 1.1<α2<α3<α4<1.3, excess air ratio: 1.4>τ1>τ2>τ3>τ4>0.6. The coal quantity and the secondary air quantity can be controlled by additionally arranging a coal quantity measuring device on each pulverized coal pipe and additionally arranging a secondary air quantity measuring device at a secondary air nozzle of the burner.
The target coal amount for the operating burner floor is shown in table 2, and the coal amount can be controlled by the rotational speed of the coal feeder.
TABLE 2 "V-shaped Combustion mode" target amount of coal for running combustor layer
Item Unit of Numerical value
Layer
1 burner layer t/h 22
Layer 2 burner layer t/h 26
Layer 3 burner layer t/h 30
Layer 4 burner layer t/h 34
The operating burner floor and the target overfire air volume are shown in table 3, and the secondary air volume can be controlled by adding air volume measuring devices at the inlets of the secondary air box and the overfire air box.
TABLE 3 "V-shaped Combustion mode" commissioning burner layer and overfire air target secondary air volume
Figure BDA0002523043970000102
Figure BDA0002523043970000111
After the V-shaped combustion mode is adopted, according to the actual situation, if the NO is possibly caused for controlling the furnace outlet NOXThe content is increased, and the air quantity distribution of each combustor of the over-fire air can be adjusted to optimize according to the actual condition. Meanwhile, the problem of coal powder burnout rate reduction which is possibly caused can be optimized by optimizing the opening degree of the folding baffle plate at the outlet of the coal mill, the rotating speed of the rotary separator and the loading force of the grinding roller according to actual conditions.
Example 2
Referring to fig. 5, a schematic diagram of a system for increasing the flue gas temperature at the inlet of a low-load SCR of a coal-fired boiler according to the present invention is shown. The system of the invention takes a tangential firing or opposed firing boiler of a power station as a research object, adjusts the distribution of the coal quantity and the secondary air quantity of each burner of a delivery burner layer, and comprises: the layering unit sprays the fire coal of the tangential firing or opposed firing boiler into the hearth for combustion by taking a layer as a unit; the coal quantity control unit is used for controlling the output of each coal feeder and further controlling the coal quantity of the layers of the delivered combustors, so that the coal quantity of each combustor layer is gradually increased from low to high along the height direction of the hearth to form positive V-shaped distribution; a coal amount metering unit; the secondary air quantity control unit is used for adjusting the secondary air quantity of each operating burner layer, so that the secondary air quantity of each burner layer is gradually reduced from low to high along the height direction of the hearth to form inverted V-shaped distribution; and a secondary air quantity metering unit.
Preferably, the coal amount measuring unit includes: the coal amount calculation unit is used for calculating the coal amount of each pulverized coal pipe through a target coal amount calculation formula of a commissioning combustor layer and a target coal amount calculation formula of each combustor of the commissioning combustor layer; the coal quantity measuring unit is additionally provided with a coal quantity measuring device on each pulverized coal pipe and is used for measuring the coal quantity of each pulverized coal pipe in real time; and the coal quantity adjusting unit adjusts the coal quantity of each pulverized coal pipe in real time by adjusting the opening of the electric valve on the adjustable shrinkage cavity of each pulverized coal pipe.
Preferably, the secondary air volume measuring means includes: the secondary air quantity calculating unit is used for calculating the secondary air quantity of each combustor through a target secondary calculation formula of a commissioning combustor layer and a target secondary air quantity calculation formula of each combustor of the commissioning combustor layer; the secondary air quantity measuring unit is additionally provided with a secondary air quantity measuring device at a secondary air nozzle of each combustor and is used for measuring the secondary air quantity of each combustor in real time; and the secondary air quantity adjusting unit adjusts the secondary air quantity of each combustor in real time by adjusting the opening of a secondary air door or the angle of a secondary air blade of each combustor.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Accordingly, the invention is not to be limited to the embodiments shown herein.

Claims (6)

1. A method for improving the low-load SCR inlet smoke temperature of a coal-fired boiler is characterized by comprising the following steps:
spraying the fire coal of the tangential firing or opposed firing boiler into a hearth for combustion by taking a layer as a unit;
calculating the coal quantity of each delivery burner layer according to a target coal quantity calculation formula of each delivery burner layer;
adjusting the coal quantity of each operating burner layer to ensure that the coal quantity of each burner layer is gradually increased from low to high along the height direction of the hearth to form positive V-shaped distribution;
calculating the secondary air volume of each operating burner layer according to a target secondary air volume calculation formula of each operating burner layer;
adjusting the secondary air volume of each operating burner layer to ensure that the secondary air volume of each burner layer is gradually reduced from low to high along the height direction of the hearth to form inverted V-shaped distribution;
calculating the coal amount of each burner according to a target coal amount calculation formula of each burner of the commissioning burner layer;
additionally arranging an electric valve on an adjustable shrinkage hole on each pulverized coal pipe of the commissioning combustor layer, and controlling the opening of the adjustable shrinkage hole to enable the coal amount of each combustor of the commissioning combustor layer to reach the target coal amount;
calculating the secondary air quantity of each burner according to a target secondary air quantity calculation formula of each burner of the commissioning burner layer;
controlling the opening degree of each burner secondary air door or the angle of a secondary air blade of each burner of the commissioning burner layer to enable the secondary air quantity of each burner of the commissioning burner layer to reach the target secondary air quantity;
the calculation formula of the target coal amount of the n-th layer of the commissioning combustor layer is as follows: cn＝C1αn，
Figure FDA0003395950760000011
n∈[1,4]Wherein, C1Indicates the target amount of coal, C, in the layer 1 combustor layernIndicates the target coal amount, alpha, of the burner floor of the nth floornA coefficient of deviation, C, of the target coal amount of the burner floor of the n-th floor from the target coal amount of the burner floor of the 1 st floorzRepresenting the total coal quantity required by the boiler, and n represents the number of layers of the operating burners;
the calculation formula of the target coal amount of each burner of the n-th operating burner layer is as follows: c. Cm＝Cn/m，m∈[1,4](ii) a Wherein m is the number of burners of the nth layer of burners;
the calculation formula of the target secondary air volume of the n-th operating burner layer is as follows: fn＝(Cnβn-Cnγn)τn(ii) a Wherein the content of the first and second substances,
Fnrepresents the target secondary air quantity, beta, of the nth burner layernRepresents the theoretical air quantity, gamma, of the burner layer of the n-th layernDenotes the air/coal ratio, tau, in the primary air-powder mixture of the n-th burner layernRepresenting the excess air factor of the nth burner layer;
the calculation formula of the target secondary air volume of each combustor of the n-th operating combustor layer is as follows: f. ofm＝Fn/m。
2. The method for increasing the inlet smoke temperature of low-load SCR of coal-fired boiler according to claim 1, characterized in that the total wind of the boilerThe formula for the calculation of the amount is: fz＝CzβzτzWherein F iszRepresents the total air quantity of the boiler, betazIndicating theoretical amount of air, τ, of the boilerzRepresenting the boiler excess air factor.
3. The method for improving the smoke temperature at the inlet of the low-load SCR of the coal-fired boiler according to claim 2, wherein the calculation formula of the burn-out air volume is as follows:
Figure FDA0003395950760000021
wherein, FrThe burn-out air volume is indicated.
4. A system for improving the smoke temperature at the low-load SCR inlet of a coal-fired boiler is characterized by comprising a layering unit, a coal quantity control unit, a coal quantity metering unit, a secondary air quantity control unit and a secondary air quantity metering unit;
the layering unit sprays the fire coal of the tangential firing or opposed firing boiler into the hearth for combustion by taking the layer as a unit;
the coal quantity control unit controls the output of each coal feeder and further controls the coal quantity of the operating burner layer, so that the coal quantity of each burner layer is gradually increased from low to high along the height direction of the hearth to form positive V-shaped distribution;
the secondary air quantity control unit controls the total secondary air door of each commissioning combustor layer so as to control the secondary air quantity of each commissioning combustor layer, so that the secondary air quantity of each combustor layer is gradually reduced from low to high along the height direction of the hearth, and inverted V-shaped distribution is formed;
the coal quantity metering unit controls the opening of the adjustable shrinkage cavity, so that the coal quantity of each burner of the commissioning burner layer reaches the target coal quantity;
and the secondary air quantity metering unit controls the opening degree of a secondary air door or the angle of a secondary air blade of each burner of the delivery burner layer, so that the secondary air quantity of each burner of the delivery burner layer reaches the target secondary air quantity.
5. The system for improving the low-load SCR inlet smoke temperature of the coal-fired boiler according to claim 4, wherein the coal amount metering unit comprises a coal amount calculating unit, a coal amount measuring unit and a coal amount adjusting unit;
the coal amount calculating unit is used for calculating the coal amount of each pulverized coal pipe through a target coal amount calculating formula of a commissioning combustor layer and a target coal amount calculating formula of each combustor of the commissioning combustor layer;
the coal quantity measuring unit is additionally provided with a coal quantity measuring device on each pulverized coal pipe to measure the coal quantity of each pulverized coal pipe in real time;
the coal quantity adjusting unit adjusts the coal quantity of each pulverized coal pipe in real time by adjusting the opening of the electric valve on the adjustable shrinkage cavity of each pulverized coal pipe;
the calculation formula of the target coal amount of the n-th layer of the commissioning combustor layer is as follows: cn＝C1αn，
Figure FDA0003395950760000031
n∈[1,4]Wherein, C1Indicates the target amount of coal, C, in the layer 1 combustor layernIndicates the target coal amount, alpha, of the burner floor of the nth floornA coefficient of deviation, C, of the target coal amount of the burner floor of the n-th floor from the target coal amount of the burner floor of the 1 st floorzRepresenting the total coal quantity required by the boiler, and n represents the number of layers of the operating burners;
the calculation formula of the target coal amount of each burner of the n-th operating burner layer is as follows: c. Cm＝Cn/m，m∈[1,4](ii) a Wherein m is the number of burners of the nth burner.
6. The system for improving the smoke temperature at the inlet of the low-load SCR of the coal-fired boiler according to claim 4, wherein the secondary air quantity metering unit comprises a secondary air quantity calculating unit, a secondary air quantity measuring unit and a secondary air quantity adjusting unit;
the secondary air volume of each burner is calculated by the secondary air volume calculating unit through a target secondary air volume calculating formula of the operating burner layer and a target secondary air volume calculating formula of each burner of the operating burner layer;
the secondary air quantity measuring unit is additionally provided with a secondary air quantity measuring device at a secondary air nozzle of each burner, and the secondary air quantity of each burner is measured in real time;
the secondary air quantity adjusting unit adjusts the secondary air quantity of each combustor in real time by adjusting the opening of a secondary air door or the angle of a secondary air blade of each combustor;
the calculation formula of the target secondary air volume of the n-th operating burner layer is as follows: fn＝(Cnβn-Cnγn)τn，n∈[1,4](ii) a Wherein, FnRepresents the target secondary air quantity, beta, of the nth burner layernRepresents the theoretical air quantity, gamma, of the burner layer of the n-th layernDenotes the air/coal ratio, tau, in the primary air-powder mixture of the n-th burner layernRepresenting the excess air factor of the nth burner layer;
the calculation formula of the target secondary air volume of each combustor of the n-th operating combustor layer is as follows: f. ofm＝Fn/m。
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